Fluid dynamic bearing device is a bearing device that rotatably supports a shaft member with an oil film that is formed in bearing clearances by relative rotation between a bearing member and the shaft member. The fluid dynamic bearing device has such characteristics as high speed rotation, high rotation accuracy, and low noise. Making the best use of those characteristics, they have been widely used in recent years as bearings intended for spindle motors to be mounted on information devices, including magnetic disk drives such as HDD and FDD, optical disc drives such as CD-ROM, CD-R/RW, and DVD-ROM/RAM, and magneto-optical disc drives such as MD and MO, polygon scanner motors to be mounted on laser beam printers (LBP) and the like, fan motors to be mounted on personal computers (PC) and the like, and small-sized motors to be mounted on electronic appliances such as axial fans.
Fluid dynamic bearings of this type are broadly classified into dynamic bearings which have dynamic pressure generating portions for generating the dynamic pressure of a fluid (such as lubricating oil) in their bearing clearances, and so-called cylindrical bearings (bearings with cylindrical bearing surfaces) which have no dynamic pressure generating portion.
For example, a fluid dynamic bearing device to be mounted on a spindle motor of a HDD or the like is provided with a radial bearing portion for supporting a shaft member in a radial direction and a thrust bearing portion for supporting the shaft member in a thrust direction. For its bearing, the radial bearing portion often uses a dynamic bearing in which two surfaces opposed across a radial bearing clearance (the outer periphery of the shaft member or the inner periphery of the bearing member) are provided with grooves for generating a dynamic pressure. Meanwhile, the thrust bearing portion may use either a dynamic bearing or a bearing that has the structure of supporting one end of the shaft member by contact (so-called pivot bearing).
Bearing member to be built into this type of fluid dynamic bearing device is composed of an inner diameter part (bearing sleeve) which has a radial bearing surface, and an outer diameter part (housing) which has a mounting surface intended for other members on its outer periphery. For the purpose of cost saving, bearing device having an outer diameter part made of a resin, such as disclosed in Japanese Patent Application Laid-Open No. 2005-114162 (patent document 1), have been proposed recently.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-114164